One apparatus of the above kind is described in the specification of French published patent application No. FR 1 497 939A, and consists of an arrangement comprising a first motorised actuator carried by a fixed structure, a linkage which includes at least on the driving or upstream side an input element which is connected to the said first actuator and which is adapted to be driven by the latter; and on the driven or downstream side of the linkage an output element which is coupled to a receptor element. The function of the receptor element is to actuate means for effecting the transition between one gear ratio and another, and/or for selecting a required gear ratio, these transition and/or selecting means being part of the gearbox and constituting the gear shifting means of the latter. The receptor element performs a movement in translation and/or rotation for changing the speed ratios of the gearbox.
Such a motorised control apparatus enables automatic gear shifting to take place in a gearbox of the kind specified above, and has the advantage, in comparison with a conventional manual gear shift system, of reducing the propagation of noises and vibrations, and also of reducing wear. In addition, gear shifting is quicker. However, such an arrangement in its known form does have the drawback that it is relatively bulky, because the actuator drives a disc which is provided with a spiral groove for controlling a receptor lever and for effecting the various gear shifting operations.
Another disadvantage of this known form of automatic gear shifting apparatus is that it is not possible, for example, to shift down directly from fourth gear to second gear, because the profile of the spiral groove prevents such a direct shift taking place. In addition, it is not possible to anticipate a gear shift. Finally, the linkage is relatively complex and is also liable to jamming.